1. Field of the Invention
The subject of the invention is an electrical supply device intended to deliver energy to a structure that includes at least two electrodes and a space containing a gas, the device comprising a voltage generator and an inductor connected to the generator and connected to the structure in order to supply the two electrodes with a periodic voltage of given frequency.
The invention will be described more particularly in the case of an electrical supply for a light source of the flat lamp type, but it may relate to any electrical supply for a structure having at least two electrodes and a gas intended to be excited, the electrodes having to be supplied with energy so as to create between them an electric field that ionizes the gas.
2. Related Art
Flat lamps are generally used for the manufacture of backlit screen devices. They consist of two glass substrates held slightly apart one with respect to the other, generally separated by less than a few millimetres, and hermetically sealed so as to contain a gas under reduced pressure, in which an electrical discharge produces radiation generally in the ultraviolet range, which excites a phosphor substance, which then emits visible light.
In a standard flat lamp structure, a glass substrate carries, on one and the same face, two screen-printed coatings, especially made of silver, in the form of interpenetrated cones constituting a cathode and an anode. This face is turned toward the space containing the plasma gas. Another glass substrate is held at a certain distance from the first by means of discretely positioned spacers and possibly a peripheral frame. A discharge (an electric field) said to be coplanar is produced between the anode and the cathode, that is to say in a direction along the main surface of the glass substrate, which discharge excites the surrounding plasma gas.
The electrodes are protected by a dielectric coating intended, by capacitively limiting the current, to prevent loss of material of the electrodes by ion bombardment near the glass substrate. At least one of the faces of the glass substrates turned toward the space containing the gas also carries a coating of phosphor material, which is excited by the ionization of the gas and thus emits light.
However, in such a structure, the electrical connectors for supplying the electrodes must pass through the sealed enclosure containing the gas, thereby requiring a complex connection system.
One solution to this connection problem is described in French patent application FR 02/10020 which discloses quite another flat lamp structure for which the electrodes are no longer placed inside the enclosure and in a co-planar manner, but on the outside and intended to generate an electric field transverse to the surface of the electrodes.
The electrodes are, for example, placed on the external face of the glass substrates opposite the gas and therefore in two separate planes. Furthermore, at least one of the electrodes is a translucent conductive element, the face that supports this electrode forming an illuminating face for the flat lamp.
Thus, placing the electrodes on the outside of the enclosure means, on the one hand, that the electrical connection is facilitated and, on the other hand, the glass substrates provide the electrodes with capacitive protection against ion bombardment of the gas.
In addition, the above structure proposes a flat illuminating element capable of providing novel options in terms of decoration, display and/or architecture.
This patent application FR 02/10020 does not describe by which means the electrodes are supplied.
One device that can be used is, for example, that given in U.S. Pat. No. 5,604,410. That supply device comprises a voltage supply source delivering a voltage in the form of a train of pulses, that is to say a voltage that periodically drops to substantially zero during a certain lapse of time. This device furthermore includes a voltage amplifier connected to the voltage source and a transformer whose primary winding is connected to the amplifier and whose secondary winding is connected to the electrodes in order to supply them.
The electrical power needed for the device of this United States patent would, especially with lamp areas close to or greater than one m2, be much too high to be delivered and also requires much too bulky a device.